As part of its mission to save lives and protect property, the National Weather Service (NWS)  issues coastal flood watches and warnings for flooding caused by extra-tropical cyclones, events which can produce storm surge and waves on top of the normal tide cycle.

To provide NWS forecasters with extra-tropical storm surge guidance, the NWS’ Meteorological Development Laboratory (MDL) uses a modified version of the Sea Lake and Overland Surges from Hurricanes (SLOSH) model (Jelesnianski et al. 1992) to predict the impacts of extra-tropical storms.  SLOSH was modified in the 1990s to:  (1) use the Global Forecast System (GFS) winds as input instead of a parametric wind model and (2) not compute overland flooding so it could run efficiently on operational computers.  The result was the Extra-Tropical Storm Surge (ETSS) model (Kim et al. 1996), which runs operationally four times daily along the Gulf of Mexico and U.S. East, West, and Alaskan Coasts.  

NWS is moving beyond the coastal flood watch and warning to develop an experimental tropical storm surge watch and warning.  Unlike the coastal flood watch and warning, the tropical storm surge watch and warning is intended to extend overland.  NWS is also considering an extra-tropical storm surge watch and warning which will extend overland.  Later, MDL has enhanced the ETSS model to compute overland flooding from surge and provide guidance for future overland extra-tropical storm surge watches and warnings.  Enhancements included:

  1. Developing a station based post-processing methodology for ETSS based on recent observations to account for model bias, sea level rise, waves, and river discharge.
  2. Nesting the tropical and extra-tropical grids to leverage both the expanse of the large extra-tropical grids and the finer overland details contained within the tropical grids.
  3. Modifying inundation calculation based on both surge and tide.
  4. Updating Alaska Basin, CONUS West coastal, East coastal and Gulf of Mexico basins.
  5. Upgrading the ETSS model to use winds with 1-hr 13k reolution.

Storm Surge

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